1. Field of the Invention
The present invention relates to a touch device, and particularly to a locating method of an optical touch device and an optical touch device that is suitable for using the locating method.
2. Description of the Related Art
Nowadays, a touch function has been one of necessary functions of many electronic devices. A touch device is an important component to achieve the touch function. Generally, a familiar type of the touch device is, for example, a resistive touch device, a capacitive touch device or an optical touch device. The electronic devices can be equipped with various touch devices in accordance with the various demands.
FIG. 1 is a schematic view of a conventional optical touch device. Referring to FIG. 1, the conventional optical touch device 100 includes a light guide module 110, a light source module 120 and an image detecting module 130. The light guide module 110 includes three light reflecting bars 112a, 112b and 112c arranged along three sides of a rectangle. The light reflecting bar 112a faces to the light reflecting bar 112c and the light reflecting bar 112b is connected between the light guide bar 112a and the light reflecting bar 112c. The area in the rectangle defines a detecting area 114. The light source module 120 includes two light emitting components 122a and 122b. The light emitting component 122a is disposed at an end of the light guide bar 112a far away from the light guide bar 112b, and the light emitting component 122b is disposed at an end of the light guide bar 112c far away from the light guide bar 112b. The light source module 120 is configured for emitting light to the three light reflecting bars 112a, 112b and 112c. The three light reflecting bars 112a, 112b and 112c are configured for reflecting the light from the light source module 120 to irradiate the detecting area 114. The image detecting module 130 includes two image detecting components 132a and 132b. The image detecting component 132a is disposed at the end of the light reflecting bar 112a far away from the light reflecting bar 112b, and the image detecting component 132b is disposed at the end of the light reflecting bar 112c far away from the light reflecting bar 112b. Each of the two image detecting components 132a and 132b includes a number of pixels 135 arranged in a straight line. The pixels 135 are configured for detecting a light blocking object (i.e., a touch point) in the detecting area 114, thereby calculating a position (i.e., coordinates) of the light blocking object in accordance with the information detected by the pixels 135.
In detail, a field of view (FOV) of the image detecting component 132a covers the light reflecting bars 112b and 112c. That is, the pixels 135 of the image detecting component 132a are configured for detecting the light reflecting bars 112b and 112c. When the light blocking object is located in the detecting area 114 and a dark point caused by the light blocking object is located at the light reflecting bar 112b, the light reflecting bar 112c, or a connecting portion of the light reflecting bar 112b and the light reflecting bar 112c, the dark point can be detected by some pixels 135 of the image detecting component 132a. Similarly, a field of view of the image detecting component 132b covers the light reflecting bars 112a and 112b. That is, the pixels 135 of the image detecting component 132a are configured for detecting the light reflecting bars 112a and 112b. When the light blocking object is located in the detecting area 114 and a dark point caused by the light blocking object is located at the light reflecting bar 112a, the light reflecting bar 112b, or a connecting portion of the light reflecting bar 112a and the light reflecting bar 112b, the dark point can be detected by some pixels 135 of the image detecting component 132b. 
Generally, the conventional optical touch device 100 calculates the position of the dark point caused by the light blocking object using either a medium center calculating method or a gravity center calculating method, thereby determining the position of the light blocking object. However, positions of the dark points caused by all light blocking objects in the detecting area 114 can not be calculated accurately using either the medium center calculating method or the gravity center calculating method. For example, in the case of using the medium center calculating method to calculate the position of the dark point, the detecting area 114 of conventional optical touch device 100 has an insensitive area 114a. If the light blocking object is just located in the insensitive area 114a, the calculated position of the dark point will generate an inaccuracy due to a large offset angle of the light. In addition, if the position of the dark point is calculated using the gravity center calculating method and the dark point caused by the light blocking object is just located at the connecting portion of two neighboring light reflecting bars, the calculated position of the dark point will generate an inaccuracy.
Referring to FIG. 2, the medium center calculating method is described in detail by using the image detecting component 132b as an example. A light blocking object A is located in the insensitive area 114a, and the image detecting component 132b is configured for detecting a dark point A1 caused by the light blocking object A. The dark point A1 is located at the light reflecting bar 112a. During a process of detecting the dark point A1, the dark point A1 can be detected by some pixels 135, for example, from the n-th pixel 135n to the r-th pixel 135r, of the image detecting component 132b. The calculated center position of the dark point A1 using the medium center calculating method is equal to (n+r)/2. That is, the center of the dark point A1 corresponds to the (n+r)/2-th pixel 135m. But, in fact, a straight line L passing through the center of the light blocking object A and the center of the dark point A1 is connected to the pixel 135m′. In other words, the accurate center of the dark point A1 should correspond to the pixel 135m′ rather than the pixel 135m. Similarly, the image detecting component 132a has the above-mentioned problem. Therefore, when the position of the dark point caused by the light blocking object in the insensitive area 114a is calculated using the medium center calculating method, the calculated position of the dark point will generate an inaccuracy.
Referring to FIG. 3, the gravity center calculating method is described in detail by using the image detecting component 132a as an example. A light blocking object B is located in the detecting area 114, and the image detecting component 132a is configured for detecting a dark point B1 caused by the light blocking object B. The dark point B1 is located at the connecting portion of the light reflecting bar 112b and the light reflecting bar 112c. During a process of detecting the dark point B1, the dark point B1 can be detected by some pixels 135, for example, from the x-th pixel 135x to the y-th pixel 135y, of the image detecting component 132a. A calculating formula of the gravity center calculating method is as follow:
  Cg  =                    ∑                  w          =          x                y            ⁢                                                            bg              ⁡                              [                w                ]                                      -                          img              ⁡                              [                w                ]                                                              ×        w                            ∑                  w          =          x                y            ⁢                                            bg            ⁡                          [              w              ]                                -                      img            ⁡                          [              w              ]                                                  
In the formula, w represents the w-th pixel, bg[w] represents a background brightness of the w-th pixel, img[w] represents an image brightness of the image detected by the w-th pixel, and Cg represents the calculated gravity center position of the dark point B1 caused by the light blocking object B. However, the conventional optical touch device 100 has poor light irradiation at the connecting portion of the light reflecting bar 112b and the light reflecting bar 112c. When the dark point B1 is located at the connecting portion of the light reflecting bar 112b and the light reflecting bar 112c as shown in FIG. 3, the background brightness and the image brightness detected by the pixels 135 of the image detecting components 132a are inaccurate. Therefore, a large error between the calculated position of the dark point B1 and the actual position of the dark point B1 will generate.
As mentioned above, the conventional locating method can not accurately calculate the position of the dark point caused by the light blocking object located in any area of the detecting area 114. Thus, the conventional optical touch device 100 can not determine the position of the light blocking object accurately.